Optimization of Composition and Heat Treating of Die Steels for Extended Lifetime

ABSTRACT

The overall objective of the program is to extend the life of die materials utilized in aluminum die casting by 50%. The main objectives of this new one-year project are: (1) to further evaluate the effect of controlled changes in steel chemistry on the resistance to heat checking, (2) develop a new fast interrupted oil-quenching cycle, and (3) verify the results of the laboratory tests with in-plant trials using production die casting machines.
The previous work has been successful, investigating a new type of die steel with a lower silicon and vanadium, and higher molybdenum content than the standard premium grade H-13 steel. The new steel was found to have a very significant improvement in thermal fatigue resistance compared to the conventional premium grade H-13. It was demonstrated that further improvement in the life of the die steels could be obtained by utilizing a rapid cooling rate from a somewhat higher austenitizing temperature during the hardening process. Finally, the research demonstrated that an optimized EDM process in shaping dies could be employed with practically no undesirable effects on the thermal fatigue resistance. (However, when the EDM process is not properly conducted, a considerable loss in thermal fatigue resistance occurs.)